As an image forming apparatus for general purpose, an inkjet recording apparatus has been known, which ejects color inks from an inkjet head and forms a desired image on a recording medium. In recent years, not only media that have permeability such as paper, but also impermeable (less-permeable) media such as resin film have been used, and an apparatus that cures the inks landed on a medium by irradiating the inks with ultraviolet light as activation light has been proposed. The ultraviolet curable inks that are applied to such an apparatus contain an initiator that has predetermined sensitivity to ultraviolet light.
In the inkjet recording apparatus to which ultraviolet curable inks are applied, a light source for ultraviolet irradiation is mounted on a carriage on which an inkjet head is mounted, the ultraviolet light source is caused to scan to follow the inkjet head, the ink droplets immediately after being landed on the medium are irradiated with ultraviolet light, and positional displacement and landing interference of the ink droplets are avoided.
Patent Literature 1 discloses a print system of an ultraviolet-curable type in which curing light sources disposed at both sides in the main scanning direction of an inkjet head are configured to be movable to a downstream side in the transporting direction of a recording medium. The print system described in Patent Literature 1 irradiates ink droplets immediately after ink deposition with ultraviolet light of a small light quantity to half cure (temporarily cure), and irradiates the ink droplets to permanently cure with ultraviolet light of a large light quantity after a lapse of a constant time.
The step of partially curing the ink to such an extent as to inhibit displacement and deformation of the ink droplets immediately after being deposited is referred to as “temporary curing”, “partial curing”, “half curing”, “pinning”, “set”, or the like. In the present description, the terms “temporary curing”, “pinning” and the like are used. Meanwhile, the step of sufficiently curing the ink by performing further ultraviolet irradiation after the temporary curing is referred to as “permanent curing” or “curing”.